Using low-voltage, unregulated DC output power from fuel cells or other unregulated power sources in distributed power systems for aircraft is an emerging technology. Current aircraft power system use a centralized power generation system, such as engine driven generators, with typical voltages of 115 VAC or 230 VAC. Emergency backup power sources of the aircraft may use low-voltage batteries. However, such backup power systems do not use power converters since the batteries are only employed to support local power buses.
Fuel cells may be used as auxiliary electric power sources on aircrafts to deliver localized and/or peak power. They may also be used as a source of emergency power. However, a fuel cell provides an unregulated DC voltage which varies with the load by as much as 50% from low-load to full-load operation. Therefore, fuel cells alone are not a valid substitute for the engine driven generators used in current aircraft since they are incapable of providing various levels and configurations of DC and AC voltages.